Water resistant leather and process of making the same



United States Patent "cc assesse WATERRES-ISTANT 5 or MAKING'THE sam No Drawing. Applicat'lotrNov einbr 1949f Seri'ziPNo. 129,s11*-"' This invention relates 'toleather and h'iore piai'ticulati'lg 15 to the treatment'ofleathertorende it-resistant to'wat'er penetration withoutdetrimental 'modification ofiits' other properties. i 3 Leather is a valuable *materia1,-' parti cula'rly fer fare manufacture of'shoe'sand other articles or clbthiiifibe- '20 cause of its pliability" and"'porosity.-"lhe peresitwis" important on two score'sk; In the firstfplac'e, 'fthe fidres are so fineas' to-be of some-valuein' givingfjmleather heat'insulating properties "Secondly, and mere-impal tant, 'whenused in shoes or other elose fittiriggai'meri' the pores .of the leather permit breathihg iaierthe escapeof water'vapor given "ot'r' by the "bodyjiandfihus r'naitW tain' the comfort-and 'healtnof the wearertfl'heathe'r however, has the disadvantage that'the fcoll ag'err fiber's" of which it is composeda're hydropltilicinnature. ccordin'gly,"water is taken up quite rapitily 'by leather- .an'd freely passes therethroug'h'; v Heretofore, because of its im ortance,ext nsive re search has been directed toward solution of th'epioblein of producing waterproof leather. These effoits havefifor the most part,"however,'"beeri directedtowardfillingthe pores 'of the leather by 'fstuflin'g' 'it' witli'oils, g'r'ea's" ,5 and/or waxes during its manufaetureyby applying" dub j bing or the like-to'finishedleather articles, "oi' by tinpregnating'it. with plastic materialssueh' as resins .or rubber. In the first"two"rn'ethods mentionew racticany no improvement-in waterproofness is obtained unlesth amount of grease, oil, wax,'or similar material placd in the pores of the leather is-so great,"abol1t 507 at more, as to completely'block thepores; 'Eveh' "with jfve y large amounts of such pore-filling inateria'ls',"the improve ment in waterproofness is of limited scope and value since it is lost when the leather is flexed. This results from the fact that; as pointed-out abovef'th'e .leather fibers are hydrophilic-and during flexing; thereforje"*the water either passesthrough the fibers "o'if' throilgl'ldlie" channels where the pore-:fill'ingmateriarh'as ptflledaway from the pore walls. I

Leather can -"be' given aratherihigh degre of wine proofnessby impregnation with --resins -"or rubuer. 'Ho ever, the resultant'produce'i's completely non-porous and; its flexibility-is also reduced. 'Botlr'th'e lattet 'inetliod and the stuffing referred to above, insofar as they block the pores of the leather,'are undesirable for many purposes, leath'er' which has been-rendered =e mp1ete1y imperviouspfor example; being-nu more suitable-for use 1 in rn'ak-ingboots and shoes than sheet rubber't I Experi ence in the armed services -an'd =el'sewherehas shown: conclusively'--the "necessity; of porosity in' roetwear and the extreme undesirability of -'using non-perous teotwesr, eVen When it is partially or wholly 'Watei'pt'oofi-except for limited periods-of time. w

An object of the present invention is, therefore? to provide leatherwhich is substantially waterproof" ander conditions of use which involve-bending and fleir'itiggyfi 7 which has a higlrdegreeof-poros-ity sdast *p'ei'rnitpa'ssage of water vaporw Another object of the invention is to provid'e 'leather which; although resistant 3 to Water '-peneti'ation is sets flexible and porous;

A further object of the invention-is to provide a process which will permit s'implification'of the methods now in use for tanning and finishing leatli'e1'!--'-' A Still another-object of the 'inventioniistto provide leather 1 which n's waterproof but is-still t fle'xible at-low tempersma tures:

Otherobjects'a're to provide a treatment for team r to render it waterproof which is inexpensive, does not mvolvelexten'sive apparatus, and is perm'a entfin effect- Addifional objeift's' 'will 'be evident" 'frorff'lthe renewing specification andclaims. 9

Applicant has made the discovery that certain deriva tives of succinic acid are effective in accomplishing the foregoing;ob.je cts. Among such derivatives thathave beeri--"f6uiid-' suitable are "'alkyla'te d 'snccinic acids; such; as alkylor alkenyl substituted succin c acids. ;The surprisiiig e'fi'ectiveness" of such compounds in waterproofing size; was extractedw-ith petroleum naphtha to removeanywax, grease, or oil. It was then treated with ;10%

of .iso-octadecenyl succinic acidin solutionin :ethyl alcohol. After the treating agent had been absorbed in the leather, the specimen was heated for about 15 minutes at men-so-treated was determined .by -a flexing test developed inthe leather-laboratory of the National Bureau of Standards which subjects .the leather to conditions which more-nearly-simulate natural use than former methods. In this -;test, the details of and apparatus for which are set .forth-in an article'by' Mieth M-aeser in the Journalof the ;-A-merican Leather Chemists Association, vol.

XLII-,-page40l, et seq.,"August 1947, leather specimens-- are continuously flexed while covered with water.

to penetrate a specimen is taken as the measure of its waterproofness.

In an article on page42 of the ASTM Bulletin for December 1947, it is .stated with reference to this flexing test:

fA large-numberof commercial shoe-upper leathers have been tested by the new method. These leathers The time or the number of flexing cyclesrequired for water:

show, in-generaL- a-low'water resistance.- The averageresistance of a large-number of samples is approximately 200;cycles -orflexes, which would correspondto walking distance of about-M; mile; -Stufiing the leather with large-quantities of grease does not greatly irnprovethe waterresistance of leatheruntilthe amount of grease exceeds '-5 0 per cent by weight Leathers having grease contents lllfiXCCSS or 50 per cent-are much more-water resistant-and may show resistances exceeding 10,000-

flexes; Suchleather; however, is not suitable for use in shoes or -garrnents because of its impermeability to water" vapor.

finding indicates that waterproofing of shoes at moderate temperatures-probably due to increased stifiness and craclemg-zofthe greases fat the reduced-temperature. This temperaturesmay be e'asier than iat reduced temperatures." fiIn general, the studies show that leather offers higher resistance to penetration by water' from the flesh side than-from the grainasi-de: The grain layer represents the principal-"water barrier-and is more easily penetrated when in the normal position due to'the higher stresses formedea't 'the creases.

Waterproofing' agents tested by the Bureau have been found to have little effect in waterproofing leather;

Among-thosetested' have :been several-of the new 'waterrepellant materials whose application to shoe-upper leather generally results in slightly reducing rather than" improvangthe water resistance; No materialhas been 1,300 fleirin eycles; EXAMPLE 2 3A sampie eeine same typeofle'ath'er" as used-in ample l' was eitractedwith'naphtha, driedj'and without 3 further treatment, subjected to test in the same manne as in Example 1. This specimen showed penetration by water in less than 50 flexing cycles. It is evident, therefore, that the treatment with the succinic acid derivative was very eifective in preventing penetration by water in the flexing test.

Other examples of leather specimens treated with alkylated succinic acids are set forth below. The speci-' mens used were all approximately 3%. x 4% inches in size.

EXAMPLE 3 A piece of upper leather was extracted with carbon tetrachloride to remove the grease, etc., and was then treated with 5% of iso-octadecenyl succinic acid in a EXAMPLE 4 A sample of army upper retan, i. e. leather which had been chrome and vegetable tanned but not stufied or impregnated with grease, oil, or wax, was treated in its usual moist condition with approximately 6% of its dry weight of iso-octadecenyl succinic acid in a carbon tetrachloride solution. After being heated at a temperature of 65 C. for approximately 2 hours in an atmosphere saturated with water vapor, the specimen was dried and was found to be quite flexible. In the Maeser flexing test, this specimen showed no penetration by water in more than-5,000 flexing cycles.

EXAMPLE 5 Another specimen of upper leather which had been chrome tanned but not vegetable tanned was treated with about of iso-octadecenyl succinic acid in solution in ethyl alcohol. After drying at 65 C., the specimen was tested in the Maeser flexing apparatus and showed no water penetration after more than 5,000 flexing cycles.

Flexing of leather in the absence of lubrication for the fibers of which it is composed produces a large amount of internal friction. The stufiing of leather has the function, aside from blocking the leather pores in an ineffectual eflort to obtain waterproofness, of providing lubrication for the leather fibers. In the tests of applicants leather waterproofed with derivatives of succinic acid it was found that in many cases, because of the small amount of treating agent used or because of an inherent lack of lubricating properties in certain of the derivatives,

the leather was insutficiently lubricated.

As a result, the internal friction of the unlubricated leather fibers during the flexing tests produced a weakening or breakdown of the leather structure which permitted water prematurely to penetrate the specimen in spite of the resistance to normal water penetration given the leather by the treating material. will be noted from the examples, in cases where the leather treated according to applicants invention with succinic acid derivatives did not appear to be sutficiently Accordingly, as

lubricated for practical use, it was further treated with a small amount of lubricant.

As the numerous tests at the Bureau of Standards,

referred to above, have conclusively shown, small amounts of ordinary lubricants for leather have no' significant etfect in preventing water penetration .of"

These prior tests were confirmed by tests made by applicant on the lubricants employed by him whichleather.

included several types of hydrocarbon oils, neats-foot oil,

glyceryl mono-oleate and oleic acid. From these tests it was determined that in no case did oil or grease lubricants alone, even when used in amounts as high as 20%.

based on the weight of the leather, give leather resistance to water penetration in the Maeser test of more than 1.75 flexing cycles.

When adequately lubricated, as for example With 10% of mineral oil, specimens treated like the specimen used in Example 3 have shown no water penetration after more than 62,000 flexing cycles. The results with substituted succinic acids of shorter chain length and thus of.

amount of a succinic acid derivative.

the addition of lubrication as shown by the following. example.

EXAMPLE 6 A specimen of finished leather extracted with carbon tetrachloride to remove the grease, wax, etc. therein was treated with 10% of n-tetradecenyl succinic acid in carbon tetrachloride solution. After heating for approximately 30 minutes at 65 C., 10% of light mineral oil was added to the specimen. .This specimen showed no water penetration after more than 7,500 flexing cycles. Even though in some cases applicants waterproofing -,derivatives of succinic acid are not themselves efiective,

(at least in the amounts necessary to give waterproofness), to provide adequate lubrication for the leather, it will be recognized that there is a great advantage in being able to provide waterproofness of leather with a small amount of a treating material and subsequently or simultaneously to obtain adequate lubrication with far smaller amounts of oilsor other lubricating materials than have been customarily used in the past. Such a dual treatment is important in connection with the waterproofing of leather to be used at low temperatures such as are encountered in Arctic regions or in the stratosphere.

Leather for such use should be flexible at low temperatures and yet at higher temperatures should be resistant topenetration by water. The ordinary oils and greases .which have previously been used to give flexibility tov .lubricating agents which are required, the porosity of leather so treated will be much higher than that of the ordinary stuffed leather. Since it is well recognized that under Arctic conditions boots and shoes must be porous so that the water vapor from the feet may be carried away" and not .freeze in the footwear, leather trelated by the dual process described above is of great va ue.

It has also been found that alkylated succinic acids can be water solubilized by reaction with volatile bases and thus leather can be treated therewith without the use of an organic solvent.

rendered water soluble by treatment with ammonia and applied in water solution to a specimen of upper leather,

degrea'sed in the same manner as in Examples 1 and 3.

During a period of heating at C. the ammonia was I driven off and the specimen was then further treated by impregnating it with 10% of mineral oil. The treated specimen showed no. water penetration in the Maeser flexing test after more than 2,100 flexing cycles.

EXAMPLE 8 A specimen of leather which had been chrome tanned and subsequently re-tanned with vegetable tanning material, but not stuffed, was treated in water with 8% of iso octadecenyl succinic acid which had been rendered Water solubleor dispersible by reaction with morpholine. Thev treated leather was kept for about 2 hours in an atmosphere saturated with water vapor at 65 C. during which time the morpholine was driven off. After drying, the specimen was subjected to the Maeser flexing test. Nowater penetration occurred with this specimen in more than. 5,000 flexing cycles.

It will be understood that alkylated succinic acids may also be applied to leather as anhydrides, hydration of the anhydrides after application producing the acid for imparting waterproofness. In the following example one method of using an anhydride is illustrated.

EXAMPLE 9 saturated with water vapor.v In; the. course of this! heat treatment. the anhydride combined with water to form. the acid. After drying, the: leather was tested for resistance to water. penetration and it was found that after more than 10,000 flexing cycles, no water had penetrated the specimen.

Also suitable for use in carrying out the ob ects: of the: present invention. are the acidor half-esters of alkylated succinic acids with both monoand polyhydric alcohols, where such half-esters have a low aflinity for water. Examples: of the use of such half-esters. follow.

EXAMPLE Aispecimen of finished upper. leather was extracted with carbon tetrachloride and was then treated with 10% of the. half-ester of isopropyl alcohol with n-octadecenyl succinic acid inv solution incarbon tetrachloride; After heating for 30 minutes at 65 C. the specimen was lubricated with 10% of light mineral oil and tested in the Maeser dynamic testing machine. The specimen showed no appreciable. water penetration after 4,000 flexing cycles.

EXAMPLE 11 A sample of leather similar to the sample. used in Example 10 was similarly extracted and was then 1mpregnated with 10% of the n-decanol half-ester of noctadecenyl succinic acid in a carbon tetrachloride solution; The specimen was kept at a temperature of 65 C. for about 2 hours in an atmosphere saturated with water vapor and, after drying, was tested for water penetration. The specimen showed no penetration of water after more than 5,000 flexing cycles.

EXAMPLE 12 EXAMPLE 13 Apiece of upper leather degreased by extraction with carbon. tetrachloride was treated with 1.01% of. the halfester of n-hexadecanol with n-decyl succinic acid in a carbon? tetrachloride solution- After heat treatment in the same. manner as in the previous example, the. leather was dried, further treated with 10% of lubricant and tested for resistance to water penetration. No penetration occurred in more than 5,000 flexing cycles.

EXAMPLE 14 A. sample of upper leather which had. been chrome and; vegetable tanned but. not stuifed was treatedby applying to it 20% of the glyceryl mono-ester of n,- octadecenyl: succinic acid in chloroform solution. After being held for 2 hours in an atmosphere saturated with water vapor at 65 C., the specimen was dried andtested. in. the Maeser machine. Water penetration was observed in less than 100 flexing cycles. The low resistance to peneration by water of the specimen is believed to be due to the fact that the mono-glycerol ester of octadecenyl succinic. acid, because of the extra hydroxyl groups in the compound, has a rather strong aflinity for water;

In the following example there is employed another glyceryl ester which, having only one hydroxyl group, is. less hyd'rophilic than the ester in the preceding example and is, therefore, elfective in. waterproofing leather.

EXAMPLE 15 Twenty percent of the halfrestersproducedby reacting glycerol mono-oleate with the anhydride of n-octadec'enyl succinic. acid. was applied in a chloroform solution to" a leather specimen of the same type asused in Example 141. After such application the leather was held. in an.

tested for water penetration. No

penetration. occurred immorethan. 13,000 flexing. cycles.

cated with 10% of oil.

. lubricated with 10% carboxyl. groups of an alkylated succinicacid with. a base.

to be quite. efiective in rendering, leather waterproof; The following senesof examples sets out a number. of"

the. tests; made with such half-soaps or salts.

EXAMPLEv 17 A specimen of finished. chrome and vegetable tanned upper leather was degreased by extraction with carbon tetrachlorideand was then treated with 10% of the potassium half-soap: of iso-octadecenyl succinic acid dissolved in: carbon tetrachloride. After heating at approximately C. for 30 minutes, the specimen was' lubricated. with 10% of oil and tested for water penetration. After more than 20,000 flexing cycles, no such penetration. had occurred.

EXAMPLE 18 The half-soap of. lithium iso-octadecenyl succinic acid was prepared and. applied in solution in carbon tetra-- chloride to' a degreased upper leather specimen in an amount equal to 10% of the weight of the leather. treatment inthe: same manner as in Example 17, the specimen was tested for water penetration in the Maeser machine and it was found that, after more than 3,500

flexing cycles, no water had penetrated the leather.

EXAMPLE 19 A piece of upper leather which had been subjected to both chrome and vegetable tanning but which had not been stuifed was treated with 15% of the lithiumhalf-soap of n.-tetradecenyl succinic acid in solution in chloroform. The specimen was then held in an atmosphere saturated with water vapor at 65 C. for about 2 hours, dried, and tested for water resistance. After more than 1,300 flexing cycles in the Maeser testing. machine, no water penetration had occurred.

EXAMPLE 20 Ten percent of the barium half-soap of iso-octadecenylsuccinic acid was applied in carbon tetrachloride; solutionto a specimen of degreased upper leather. men, after heating for 30 minutes at 65 C., was lubri- In the-Maeser water penetration test, the specimen was subjected to more than 23,000- flexmg cycles without water penetration.

EXAMPLE 21 A sample of degreased upper leather was treated with 10% of the cadmium half-soap of iso-octadecenyl succinic acid in a carbon tetrachloride solution. The specimen was dried at 65 C. for 30 minutes and was thenof oil. No water penetration was found after more: than 41,000 flexing cycles.

EXAMPLE 22 A degreased upper leather specimen was treated with 10% of the half-soap produced by reacting lead. acetate in. the Maeser test, no penetration occurring after more than 2,500 flexing cycles.

EXAMPLE'23 A piece of upper leather degreased with carbon tetrachloride was treated with 5% of its weight of the zinc half-soap of iso-octadecenyl succinic acid dissolved in carbon tetrachloride. After driving off the solvent during heating for about 30 minutes at 65 C., the specimen was tested: for water penetration. No penetration occurred. in. more than 2,000 flexing cycles.

It. was thendried and was re-testedin.

After The speci- EXAMPLE 25 Five percent of the zinc half-soap of iso-octadecenyl succinic acid was applied in a carbon tetrachloride solution to a piece of degreased leather. The solvent was driven olf during heating for 30 minutes at 65 C. The treated leather was then further treated by the application of of oil as a lubricant and tested in the Maeser machine for waterproofness. After more than 60,000 flexing cycles, no water had penetrated the leather.

EMMPLE 26 A piece of degreased upper leather was-saturated with a carbon tetrachloride solution containing 10% of the weight of the leather of the aluminum half-soap of isooctadecenyl succinic acid. The treated specimen was heated at 65 C. for 30 minutes and was then lubricated with 10% of oil. In the Maeser flexing test, no penetration of the leather by water occurred in more than 2,500 flexing cycles.

EXAMPLE 27 The mixture of half-soaps produced by reacting a long chain aliphatic secondary amine with a mixture of ndecenyl and n-dodecenyl succinic acids was dissolved in chloroform and a piece of degreased upper leather was saturated with sufficient of the solution to leave approximately 10% of the reaction product in the leather. After being heated at 65 C. in an atmosphere saturated with water vapor for 2 hours, the specimen was dried and lubricated with 10% of oil. In the Maeser testing machine no water penetration of the leather occurred after more than 1,300 flexing cycles.

As previously mentioned, the permeability of leather to water vapor is of great importance where the leather is used in making articles of clothing such as shoes. Where leather is treated in accordance with the usual procedure by stufiing so that large: amounts of oil, grease, and/or wax fill the pores of the leather, the water vapor permeability is very low. In the following table, the permeability of upper leather treated in various ways is shown, the figures given being the grams of water as vapor passing through the leather specimens in a period of 100 minutes under the same controlled conditions. The results of Maeser flexing tests on these samples are also given.

Table Water Vapor, Water Penetration, grams/100 Flexlng cycles min.

Stuffed leather .084 Less thanlOO. Heat treated stuffed leather 026 Do. Degreased leather, heat treated 481 D0. Degreased leather treated with of .365 More thanl,300.

iso-octadecenyl succinic acid and then heat treated.

1 Test stopped after 1 5 minutes with no penetration.

The heat treatment, referred to in the table consisted in heating the leather to approximately 65 C. for 30 minutes. The degreased leather was obtained by repeatedly extracting stufled leather w th petroleum naphtha. The iso-octadecenyl succinic acid wasapphecl s same leather heat treated had significant resistance to water penetration. On the other hand, the degreased leather which had been treated in accordance with the present invention had, even after heat treatment, a permeability which was more than as great as that of the degreased leather and a high resistance to water penetration.

It will be evident, therefore, that the treatment of leather in accordance with the present invention to render it resistant to water penetration is extremely valuable since the water vapor permeability of leather so treated is many times greater than that of stuffed leather which is ordinarily used.

.The resistance to water penetration imparted to leather by impregnating it with derivatives of succinic acid in accordance with the present invention is maintained over Icing periods of time as shown by the following examp es:

EXAMPLE 28 The specimen of Example 1, after storage for over six months at room temperatures with varying humidity conditions, was, without any further treatment, re-tested in the Maeser machine. No water penetration was observed after more than 5,000 flexing cycles.

EXAMPLE 29 The specimen of Example 5, after storage for over six months at room temperatures with varying humidity conditions, was, without any further treatment, re-tested for resistance to water penetration. No penetration was observed after more than 5,000 flexing cycles.

As pointed out above, alkylated succinic acids, as well as the half-esters and half-soaps or salts thereof may be used in carrying out the waterproofing of leather in accordance with the present invention. However, as was previously mentioned, the derivatives of succinic acid used must have a very low afiinity for water in the form in which they remain in the leather. The longer chain length alkylated acids are quite satisfactory in this respect and it is possible, as shown in the foregoing examples, to form with alkylated acids having shorter carbon chains half-esters or half-soaps which are very effective.

While not intending to be bound by any theory concerning the manner in which the succinic acid derivatives produce waterproofness of leather, it is believed, from observation of the many tests which have been carried out, that a reaction occurs between the free carboxyl group or groups of the succinic acid derivatives and either the fibers of the leather or, in certain cases, with the chrome or other metal complex which has been produced in the leather by reaction of chrome or other rajetal tanning solutions with the collagen of the leather ers.

Regardless of what the actual action is, the succinic acid derivatives are firmly held in the leather. Referring back to Examples 15 and 16, it will be seen that the treated specimen, after being boiled in water, was still very resistant to water penetration. Other specimens have, after impregnation with succinic acid derivatives,

been extracted with organic solvents and found to still be so water resistant as to show no penetration by water in the Maeser test after thousands of flexing cycles as, for instance:

EXAMPLE 30 acid derivatives, in accordance with the present invention, the leather fibers have been changed by rendering their surfaces hydrophobic instead of hydrophilic. Support is given to this conclusion by the fact that when oil as a lubricant is applied to leather which has been waterproofed by previous treatment with succinic acid derivatives, the oil is absorbed and spreads in the leather much more readily than it does with untreated leather. Such behavior is strong evidence that the leather fibers have been rendered oil receptive.

As a result of this change in the surface character of better lubricationof the leather fibers, will result in the leather having improvediwearingqualityi It has also been found that the succinic acid derivatives employed for waterproofing leather are' effective to inhibit the fbrowth of fungi on theleather wheniit is :exposed to .moist atmospheres for prolonged periods of time. characteristic is important as the mildewing or molding .of. leather is a serious problem in damp climates where This the use of waterproofleather'will often be required.

" In the article referred to above describing the -Maeser testing machine, it will be noted that the Maeser test also involves atxdetermination ofthe weight of water penetrating the leather during a predetermined number ,of flexing cycles. No figures are available on the amount of water penetrating the samplesmentioned in the examples given above,.since in only a few cases had any water penetrated the specimen of leather before the test :was stopped. Since, by applicants invention itis possible to produce porous leather which is wholly impenetrable by water under the conditions of the'Maeser test for periods of time so much longer than any leather heretofore known, the amount of water which may eventually pass through the leather is a negligible factor in the usefulness of the treated leather.

In treating leather in accordance with the present invention to render it waterproof, the succinic acid derivatives employed may be applied to the leather in a number of different ways, the choice of which depends upon the condition of the leather, the apparatus available, and the type of succinic acid derivative used. Thus, in some instances, application of alkylated succinic acids or their anhydrides solubilized with ammonia, morpholine, or other similarly volatile base, may be employed where it is desired to avoid the use of organic solvents. The succinic acid derivatives used are all soluble in an organic solvent such, for example, as carbon tetrachloride, chloroform, trichlorethylene and alcohol and may, therefore, be applied very conveniently in solution. In other cases, water emulsions of the treating agents may be used, or, where the succinic acid derivatives or their respecltive anhydrides are liquids, they may be applied direct y.

Any lubricant which may be desired or necessary for the leather may be applied before, after, or in conjunction with the succinic acid derivatives employed. The lubricant must, of course, be water insoluble, since otherwise it would not be permanent, but it may be applied as such or may be applied in solution in an organic solvent or as an emulsion in Water. It is to be noted that stuffed leather, without extraction of the oil, grease, etc., incorporated therein, can be rendered very resistant to water penetration by treatment with applieants water proofing materials. Since, however, the permeability to water vapor of the stuffed leather is already very low, the usefulness of such treatment is small.

It has been determined by research workers in the leather field that autoxidation of lubricants present in the leather to form peroxides and low molecular weight water soluble acids is one of the principal causes for the deterioration of leather. Oxidation may also cause breakdown or decomposition of certain of the succinic acid derivatives which may be used in the waterproofing of leather. The stability of such lubricants and derivatives may be increased and their breakdown or oxidation retarded or completely prevented by the incorporation of a small amount of an anti-oxidant. An anti-oxidant which is particularly suitable for this use because of its lack of odor and color is 2,6-di-tert-butyl-para-cresol. The stability of the succinic acid derivatives may also be increased in many cases by hydrogenation thereof.

it will be seen from the foregoing that the method of treating leather with the waterproofing compounds ..tribution therein. .reaction of the treating agent with the leather or tan- .ningmaterials which does occur is promoted or hasleather, after application of the succinic acid deriva- .tive being used for waterproofing-has been found ad- .vantageous for this purpose.

It is believed that the heating assists the spreading of the treating agent throughout the leather and this insures its uniform dis- It is also considered likely that any tened by the heating.

In many cases, it is desirable to prevent drying of the leather during heating and, as will be noted above, the heating may in such cases be carried out in an atmosphere saturated with Water vapor. While the temperature of such heating when used, is not critical so far as theinvention is concerned, the use of very high temperatures must, of course, be avoided since the leather would be damaged thereby. When heating leather to which a succinic acid derivative has been ap- .plied for Waterproofing, it is particularly important that 20 the leather should not betheated above the temperature at which it will shrink. .The shrinkage temperature of leather varies in accordance with the tanning-process which has been used and, accordingly, the heating temperatures permissible in any particular case will depend upon the type of leather and the previous tanning treatment.

The amounts of succinic acid derivatives which have been found most effective in rendering leather resistant to water penetration vary to some extent with the type of leather and the particular succinic acid derivative employed. Good results, however, have been obtained with amounts as low as 2%, based on the original weight of the leather, although with such low amounts of treating agent additional lubricant is always necessary to make the leather pliable.

The use of succinic acid derivatives in amounts greater than 15% to 20% of the weight of the leather has not been found to add materially to their effectiveness in preventing water penetration of leather. Therefore, although the use of larger amounts is not deleterious from the standpoint of water penetration, it is in most cases undesirable since the high permeability to water vapor of leather treated in accordance with the present invention will obviously be somewhat reduced if amounts of treating material larger than necessary for imparting resistance to water penetration are put into the leather.

The leather used in the examples of this application has been leather of the type used for shoe uppers since the Maeser testing machine is particularly adapted for determining the resistance of such leather to water penetration. Other types of leather are, however, susceptible to treatment in accordance with the present invention to make them waterproof. Thus, a shoe can be made in which not only the uppers, but also the sole are impenetrable by water and other leather products can be made waterproof.

In the foregoing specification, there has been described applicants novel and useful method of producing highly porous leather which is extremely resistant to Water penetration even under the severe conditions imposed by the Maeser testing machine. It will be understood that the invention is to be construed broadly and that failure to specifically point out all of the applications thereof which will be apparent to those skilled in the art is not intended as an abandonment thereof. On the contrary, it is intended that the invention should only be limited by the appended claims.

What is claimed is:

l. The method of making leather resistant to water penetration which comprises introducing into the leather a monomeric, acidic succinic acid derivative having low Water solubility selected from the group consisting of succinic acids and the anhydrides, half-esters and halfsoaps of said succinic acids, said derivative containing an organic hydrophobic waterproofing group substituted on a non-acidic carbon atom of succinic acid.

2. The method according to claim 1 wherein the succinic acid derivative is alkylated.

3. The method of making leather resistant to water penetration which comprises introducing into the leather an alkylated succinic acid having low water solubility.

4. The method of making leather resistant to water penetration which comprises introducing into the leather a half-ester of an alkylated succinic acid having low Water solubility.

5. The method of making leather resistant to water penetration which comprises introducing into the leather a half-soap of an alkylated succinic acid having low water solubility.

6. The method of making leather resistant to water penetration which comprises introducing into the leather the anhydride of an alkylated succinic acid which has low water solubility.

7. Leather impregnated with a monomeric, acidic succinic acid derivative having low water solubility and selected from the group consisting of succinic acids and the anhydrides, half-esters, and half-soaps of said succinic acids, said derivative containing an organic hydrophobic waterproofing group substituted on a non-acidic carbon atom of succinic acid.

8. Leather according to claim 7, wherein the succinic acid derivative is alkylated.

9. Leather impregnated with an alkylated succinic 20 acid having low water solubility.

10. Leather impregnated with a half-ester of an alkylated succinic acid having low water solubility.

11. Leather impregnated with a half-soap of an alkylated succinic acid having low water solubility.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,066,125 Rozenbroek Dec. 29, 1936 2,115,509 Jaeger Apr. 26, 1938 2,118,308 Jaeger May 24, 1938 2,123,832 Jaeger July 12, 1938 2,425,828 Retzsch Aug. 19, 1947 2,442,672 Von Fuchs June 1, 1948 2,458,425 Rocchini Jan. 4, 1949 FOREIGN PATENTS Number Country Date 699,845 Germany Dec. 7, 1940 OTHER REFERENCES Ruppenthal et a1., abstracted in Jour. Amer. Lea. Chem, vol. 38, pp. 148-168; pages 151, 157, 162 and 163 are of interest. 

1. THE METHOD OF MAKING LEATHER RESISTANT TO WATER PENETRATION WHICH COMPRISES INTRODUCING INTO THE LEATHER A MONOMERIC, ACIDIC SUCCINIC ACID DERIVATIVE HAVING LOW WATER SOLUBILITY SELECTED FROM THE GROUP CONSISTING OF SUCCINIC ACIDS AND THE ANHYDRIDES, HALF-ESTERS AND HALFSOAPS OF SAID SUCCINIC ACIDS, SAID DERIVATIVE CONTAINING AN ORGANIC HYDROPHOBIC WATERPROOFING GROUP SUBSTITUTED ON A NON-ACIDIC CARBON ATOM OF SUCCINIC ACID. 